Longitudinally joined superconducting resonating cavities

ABSTRACT

A system and method for fabricating accelerator cavities comprises forming at least two half cavities and joining the half cavities with a longitudinal seal. The half cavities can comprise at least one of aluminum, copper, tin, and copper alloys. The half cavities can be coated with a superconductor or combination of materials configured to form a superconductor coating.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 15/656,509, entitled “LONGITUDINALLY JOINED SUPERCONDUCTINGRESONATING CAVITIES,” filed Jul. 21, 2017, which claims the priority andbenefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent ApplicationSer. No. 62/364,975, filed Jul. 21, 2016, entitled “LONGITUDINALLYJOINED SUPERCONDUCTING RESONATING CAVITIES.” U.S. patent applicationSer. No. 15/656,509 and Provisional Patent Application Ser. No.62/364,975 are herein incorporated by reference in their entirety.

STATEMENT OF GOVERNMENT RIGHTS

The invention described in this patent application was made withGovernment support under the Fermi Research Alliance, LLC, ContractNumber DE-AC02-07CH11359 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

BACKGROUND

Radio-frequency (RF) cavity resonators are a fundamental component inparticle accelerators. RF cavity resonators are used to acceleratecharged particles via resonant electromagnetic fields therein.

Prior art RF cavity resonators are made from an electrically conductivematerial, and generally include one or more specially shaped chambers.Each chamber shape is explicitly chosen according to the desiredresonance conditions for the application. Prior art cavity resonatorswere, at one time, formed from copper. More recently, however, coppercavities have increasingly been replaced by cavities formed fromsuperconducting material, in order to provide a more attenuated beam.

In some cases, RF cavity resonators are manufactured from niobium metal.niobium is refractory and requires highly convergent electron or laserbeams to create the high-purity fully penetrating weld necessary toensure the cavity is vacuum tight. In general, cavity geometry has axialsymmetry. Thus, in prior art, system components are usually rotatedunder a fixed focal location of the weld beam in order to join parts ofthe cavity. As a result, certain seam geometry in a niobium cavity isnot possible because of the difficulty in translating either the part orthe focal position along the undulating profile of the cavity.

While RF resonator cavities formed from superconducting materials arevery useful for a number of applications, they are also very difficultto assemble, disassemble, and/or reassemble because the materialsinvolved generally have extraordinarily high melting points. As aresult, in some prior art approaches circumferential seams are used tomanufacture a cavity. Such circumferential seams alter thecharacteristics of the RF current present in the cavity and in turnnegatively affect particle acceleration.

As such, improved methods and systems for joining pieces used to form RFcavity resonators are required.

BRIEF SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the embodiments disclosed and isnot intended to be a full description. A full appreciation of thevarious aspects of the embodiments can be gained by taking the entirespecification, claims, drawings, and abstract as a whole.

It is, therefore, one aspect of the disclosed embodiments to provideradio frequency (RF) resonating cavities.

It is another aspect of the disclosed embodiments to provide methods andsystems for assembling RF resonating cavities.

It is another aspect of the disclosed embodiments to provide a methodand system for joining one or more sections of RF resonating cavities.

It is another aspect of the disclosed embodiments to provide methods andsystems for improved assembly of RF resonating cavities utilizinglongitudinally joined sections of the RF resonating cavities.

For example, in the embodiments disclosed herein, a method forfabricating accelerator cavities comprises forming at least two piecesof an RF resonating cavity and joining the at least two pieces of the RFresonating cavity with a longitudinal seal thereby forming an RFresonating cavity. The pieces of the RF resonating cavity can compriseat least one of aluminum, copper, tin, and copper alloys. The at leasttwo pieces of the RF resonating cavity can be coated with asuperconductor which can include niobium, MgB₂, and Nb₃Sn. In certainembodiments, the RF resonating cavity can be heat treated in order tomanipulate the characteristics of the coating. In other embodiments,patterning and lithographic processes can be applied to surfaces of theRF resonating cavity to tailor an electric field configuration therein.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the embodiments and, together with the detaileddescription, serve to explain the embodiments disclosed herein.

FIG. 1 illustrates a multi-cell RF resonating cavity formed with alongitudinal seam in accordance with the disclosed embodiments;

FIG. 2A illustrates a half-cell of an RF resonating cavity in accordancewith the disclosed embodiments;

FIG. 2B illustrates a single celled RF resonating cavity formed with alongitudinal seam in accordance with the disclosed embodiments;

FIG. 3 illustrates a single celled RF resonating cavity with associatedelectro-magnetic fields in accordance with the disclosed embodiments;

FIG. 4A illustrates a half-cell of an RF resonating cavity in accordancewith the disclosed embodiments;

FIG. 4B illustrates a single celled RF resonating cavity formed with alongitudinal seam in accordance with the disclosed embodiments;

FIG. 5A illustrates a block diagram of a deposition source associatedwith the manufacture of an RF resonating cavity in accordance with anembodiment;

FIG. 5B illustrates a block diagram of a rotating deposition sourceassociated with the manufacture of an RF resonating cavity in accordancewith an embodiment;

FIG. 6 illustrates a flow chart of steps associated with a method formanufacturing an RF resonating cavity, in accordance with an embodiment;

FIG. 7 illustrates a flow chart of steps associated with an additionalmethod for manufacturing an RF resonating cavity, in accordance with anembodiment;

FIG. 8 illustrates a flow chart of steps associated with an additionalmethod for manufacturing an RF resonating cavity, in accordance with anembodiment;

FIG. 9 illustrates a flow chart of steps associated with an additionalmethod for manufacturing an RF resonating cavity, in accordance with anembodiment;

FIG. 10 illustrates a flow chart of steps associated with an additionalmethod for manufacturing an RF resonating cavity, in accordance with anembodiment;

FIG. 11 illustrates a flow chart of steps associated with a method forjoining pieces of a non-superconducting RF resonating cavity, inaccordance with an embodiment;

FIG. 12 illustrates a flow chart of steps associated with a method forjoining pieces of a superconducting RF resonating cavity, in accordancewith an embodiment;

FIG. 13 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment;

FIG. 14 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment;

FIG. 15 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment;

FIG. 16 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment;

FIG. 17 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment; and

FIG. 18 illustrates a flow chart of steps associated with an additionalmethod for joining pieces of a superconducting RF resonating cavity, inaccordance with an embodiment.

DETAILED DESCRIPTION

The particular values and configurations discussed in the followingnon-limiting examples can be varied, are cited merely to illustrate oneor more embodiments, and are not intended to limit the scope thereof.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments are shown. The embodiments disclosed herein can be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the embodiments to those skilled in the art. Likenumbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning.Likewise, the phrase “in one embodiment” as used herein does notnecessarily refer to the same embodiment and the phrase “in anotherembodiment” as used herein does not necessarily refer to a differentembodiment. It is intended, for example, that claimed subject matterinclude combinations of example embodiments in whole or in part.

In general, terminology may be understood at least in part from usage incontext. For example, terms such as “and,” “or,” or “and/or” as usedherein may include a variety of meanings that may depend at least inpart upon the context in which such terms are used. Typically, “or” isused to associate a list, such as A, B, or C, is intended to mean A, B,and C, here used in the inclusive sense, as well as A, B, or C, hereused in the exclusive sense. In addition, the term “one or more” as usedherein, depending at least in part upon context, may be used to describeany feature, structure, or characteristic in a singular sense or may beused to describe combinations of features, structures, orcharacteristics in a plural sense. In addition, the term “based on” maybe understood as not necessarily intended to convey an exclusive set offactors and may, instead, allow for existence of additional factors notnecessarily expressly described, again, depending at least in part oncontext.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

In accordance with the embodiments disclosed herein, RF resonatingcavities, such as RF resonating cavity 105, generally comprise achamber, or series of closed chambers, as shown in FIG. 1 . FIG. 1illustrates a side view of a series of closed resonating cavities 105that form a multi-cell RF resonating cavity 100. FIG. 1 also provides ahead on view of an RF resonating cavity 105.

The RF resonating cavities 105 associated with the multi-cell RFresonating cavity 100 can be made from electrically conductivematerials, superconducting materials, or some combination thereof,including coating a shell 115 of the resonating cavities 105 with adesired material.

The multi-cell RF resonating cavity 100 can be used to acceleratecharged particles along the alignment axis of the cavity illustrated byarrow 120. Electrical currents, which result from accelerating waves,tend to run along the interior walls of the multi-cell RF resonatingcavity 100 in the direction defined by the axis of acceleration. Theembodiments disclosed herein provide improved methods and systems forforming RF resonating cavities, such as multi-cell RF resonating cavity100.

FIG. 2A illustrates a half-cavity piece, or “half-cell blank” 200, of anRF resonating cavity chamber 105 in accordance with the systems andmethods disclosed herein. Two identical half-cell pieces, such ashalf-cell blank 200, comprise the opposing halves of an RF resonatingcavity 105 that can be joined by a longitudinal seam 110, in accordancewith the disclosed embodiments. The half-cell blank 200 can be producedusing punch and die stamping of a copper sheet or other such knownmeans. It should be understood that in certain embodiments, multi-celledhalf-cell blanks associated with a series of chambers 105 can be used tocreate a multi-cell RF resonating cavity, such as multi-cell RFresonating cavity 100.

Longitudinal seams can be used to connect, close, and/or seal multiplepart-cavity pieces (i.e., two half-cell blanks 200) in order to form acompleted resonating cavity chamber 105 or multi-cell RF resonatingcavity chamber 100. Joining two half-cell blanks 200 can include avacuum seal that can be produced by welding, brazing, soldering, orother bonding techniques, as appropriate for the choice of electricallyconductive material. It should be understood that, any of these andother joining methods may be used for the joining of cavity pieces asdescribed herein. In such embodiments, the longitudinal seam (or seals)110 can be formed by such joining procedures.

FIG. 2B illustrates two half-cell blanks 200 joined with a longitudinalseam 110, thereby forming a single celled RF resonating chamber 305according to the methods disclosed herein, in accordance with thedisclosed embodiments. In the embodiment illustrated in FIG. 2B, thebeam tubes 205 are seamless. In other embodiments, the beam tubes 205can similarly be joined using a longitudinal seam as described herein.FIG. 2B also illustrates flange 210 which may form a part of the RFresonating cavity in certain embodiments.

In other embodiments, a multi-cell RF resonating cavity 100 can beformed according to the same method illustrated in FIGS. 2A and 2B,which shows the means for manufacturing a single celled resonatingchamber 305. In such embodiments, one or more longitudinal seams 110 canbe used to join multi-cell half-cavity blanks to form a multi-celled RFresonating chamber (e.g., multi-cell resonating cavity chamber 100).

The longitudinal seams 110 represent a significant improvement overpreviously used manufacturing methods for RF cavities. The longitudinalseam prevents interfaces that obstruct oscillating currents in the cellstructure, thereby improving the efficiency of the resonating cavity 305formed according to the manufacturing methods described herein.

FIG. 3 illustrates the electric field 310, magnetic field 315, andelectric current 320 as they are oriented in the chamber 305. Asillustrated in FIG. 3 , an induced electric current 320 runs along thelongitudinal axis of the chamber 305 under the application of anelectric field 310 and its associated magnetic field 315. The electricfield 310 provides particle acceleration. Fundamental laws of physicsrequire an orthogonal magnetic field 315, and these mutual forcesdetermine the orientation of induced current 320 along the chamber 305surface.

In order to produce the desired particle acceleration, the electricfield 310 must be aligned with the axis of the RF resonating cavity 305,along which the beam of charged particles moves. The applied electricfield 310 is thus used to accelerate particles through the RF resonatingcavity 305 in the desired direction.

By manufacturing the RF resonating cavity 305, according to the methodsdescribed herein, with a longitudinal seam 110, the induced RF current320 does not cross the longitudinal seam 110. Unlike prior artmanufacturing schemes, the longitudinal seam 110 does not run around thecircumference of the RF resonating cavity 305, and thus, does not crossthe path of the RF current 320. As a result the completed surface of theRF resonating cavity 305 does not alter the characteristics of the RFcurrent and does not negatively affect the particle acceleration.

FIG. 4A illustrates a half-cell with tubes blank 400 in accordance withthe embodiments disclosed herein. Two identical half-cell pieces, suchas half-cell with tubes blank 400 comprise the opposing halves of an RFresonating cavity 405 with integrated beam tubes 410 joined by one ormore longitudinal seams 110. FIG. 4A is provided to illustrate the easeof manufacture using the embodiments described herein. In particular,many cavities can be fabricated using one die and one geometry ofstamped material. In another embodiment, a plurality of cells (such asmulti-cell cavity 100) can be fabricated using one die and one geometryof stamped material to form a multi-cell cavity, sealed with alongitudinal seam.

FIG. 4B illustrates a manufactured RF resonating cavity 405 formed byjoining two identical half-cell with tubes blanks 400. The half-cellwith tubes blanks 400 can be joined with a single longitudinal seam 110.Flanges 415 can further be configured onto the ends of the half-cellwith tubes blanks 400.

As with the embodiments disclosed above, the longitudinal seam 110 doesnot cross the induced RF current present in the RF resonating cavity405. It should be understood that, although FIG. 4B illustrates a singlecelled RF resonating cavity, in other embodiments multiple cavity cellscould likewise be joined with a single longitudinal seam.

Joining half cavity pieces, or cavity pieces of other sizes withlongitudinal seams as disclosed improves the ease of manufacturing RFresonating cavities. RF resonating cavities are generally formed of asuper conducting material. For example, in some embodiments, half-cavityand part-cavity pieces can be fabricated by ordinary stamping or deepdrawing of a material such as copper. The interior surfaces of thestamped blank can be subsequently coated with a superconductingmaterial.

FIG. 5A illustrates line of sight coating of a half-cell blank such ashalf-cell blank 515 in accordance with the methods and systems disclosedherein. In such embodiments, the half-cell blank 515 can be formed fromcopper (or other such material) and can be fabricated by stamping, deepdrawings, or other such technique. A source 505 can emit, spray, orotherwise dispense coating 510. The source 505 can, for example, employvacuum plasma spraying to directly form a superconductor coating on theexposed surface of the half-cell blank 515. The source 505 can be aimedat, for example, an unassembled half-cell blank 515 or series ofhalf-cell blanks 515. In certain embodiments, illustrated in FIG. 5B,the source 505 and/or blank 515 can be rotated, as illustrated by arrow520, in order to provide coating on the desired portions of thehalf-cell blanks 515. The rotation ensures that a uniform coating can beapplied to all portions of the half-cell blank 515.

The coating 510 can be a superconducting coating. In some embodiments,reactant precursors can be applied and the superconductor can be formedduring a subsequent process such as a heat treatment cycle. In suchembodiments, joining part-cavity pieces can precede the formation of thesuperconductor, in which case it may be possible to simultaneously formthe vacuum seal as well as carry out a reaction that forms thesuperconducting material. This reaction may additionally serve to healany seam.

A superconducting metal, such as pure niobium, can be applied, forexample, by vacuum plasma spraying to directly form the superconductorcoating. Alternatively, a plurality of materials, such as layers ofniobium and bronze (a solution of tin in copper), can also be applied tothe half-cell blank 515 to form a complex superconductor, such as Nb₃Sn(triniobium stannide), also called “niobium stannide” or “niobium tin”in common trade, after the heat treatment is applied.

FIGS. 6-10 illustrate methods associated with the embodiments disclosedherein. In FIG. 6 , a method 600 for creating a niobium on coppersuperconducting cavity is illustrated. The method begins at step 605. Acopper blank can be formed as shown at step 610. The copper blank cancomprise at least two cell pieces. For example, the copper blank cancomprise two half-cell pieces. The cell pieces may also comprisemulti-cell half-cell pieces. The cell pieces can be coated with niobiummetal at step 615. The opposing half-cell pieces can then be joined withlongitudinal seams as shown at step 620 in order to form asuperconducting cavity. In some embodiments, brazing or other suchmechanisms can be used to join the cell pieces. It should be understoodthat the niobium coating forms an over-coating that produces physicalcontact across the seam. The method ends at step 625.

In another embodiment, FIG. 7 illustrates a method 700 for creating asuperconducting RF resonating cavity by direct deposition. In thisembodiment, the method begins at step 705, after which, a copper blankcan be formed as shown at step 710. The copper blank can comprise atleast two cell pieces, such as, for example, opposing half-cell pieces.The half-cell pieces may also comprise multi-cell half-cell pieces. Thehalf-cell pieces can be coated with superconducting materials such asNb₃Sn, MgB₂, or other high-temperature superconductors including V₃Ga,Nb₃Al, FeSe_(0.5)Te_(0.5), and Ba_(0.6)K_(0.4)BiO₃, and Nb₃Sn as shownat step 715. The opposing half-cell pieces can then be joined withlongitudinal seams at step 720, in order to form a superconductingcavity. Again, the overcoating can produce physical contact across theseam. In certain embodiments, a post treatment can also be applied tofacilitate consolidation and bonding of the coating. The method ends atstep 725.

In another embodiment, illustrated in FIG. 8 , a method 800 is describedfor forming an Nb₃Sn coating on a copper cavity. The method begins atstep 805. At step 810, a copper blank can be formed. The copper blankcan comprise at least two cell pieces. The cell pieces can compriseopposing half-cell pieces or can comprise half multi-cell pieces inaccordance with design considerations. The cell pieces can be coatedwith one or more layers of tin and niobium as shown at step 815.

Next at step 820, the coated cells can be heat treated with a heatprofile ranging from 200-700 degrees C. The heat treatment temperaturecan be selected according to the type of coating and/or material of thecells. The heat treatment facilitates a direct reaction between the tinand niobium, resulting in the formation of Nb₃Sn. The reaction causes anexpansion of the Nb₃Sn, which fills in gaps at the seams between thecell pieces. The cell pieces can then be joined with longitudinal seamin order to form a superconducting cavity at step 825. It should beappreciated that in alternative versions of the method 800, the cellpieces can be joined before heat treatment. The method ends at step 830.

In an alternative embodiment of FIG. 8 , the heat treatment illustratedat step 820 can be performed in multiple stages. First, the cell piecescoated in tin can be heated to between 200 and 500 degrees C. Thisallows the tin to mix with the copper to form bronze. The bronze-coatedcell pieces can be subsequently re-coated with niobium. The re-coatedhalf-cell pieces can then be heated to between 500 and 1200 degrees C.The bronze then reacts with niobium to form superconducting Nb₃Sn. Theopposing half-cell pieces can then be joined with longitudinal seams inorder to form a superconducting RF resonating cavity. In an alternativeembodiment, the cell pieces can also be joined with a longitudinal seambefore the final heat treatment cycle, in order to form thesuperconducting RF resonating cavity.

In another embodiment illustrated in FIG. 9 , a method 900 isillustrated for creating a superconducting cavity of Nb₃Sn on copper viaa bronze-niobium reaction with a diffusion barrier. In this case, themethod begins at step 905. At step 910, a copper blank can be formed.The copper blank can comprise at least two cell pieces. The cell piecescan be, for example, opposing half-cell pieces or half multi-cellpieces.

As illustrated at step 915, the cell pieces can be coated withsequential layers of niobium, bronze, and niobium. The coated cells arethen subject to a heat treatment cycle at step 920 where the coatedcells are heated to between 600 to 1200 degrees Celsius. The heattreatment facilitates reaction between the layers resulting in theformation of superconducting Nb₃Sn. The cell pieces can then be joinedwith longitudinal seams as shown at step 925 in order to form asuperconducting RF resonating cavity. The method ends at step 930. Itshould be appreciated that, in an alternative embodiment, the cellpieces can be joined before the heat treatment cycle.

In yet another embodiment, FIG. 10 illustrates a method 1000 forcreating a superconducting cavity of MgB₂ on copper via magnesium-copperand magnesium-boron reactions. The method begins at step 1005. A copperblank can be formed at step 1010. The copper blank can comprise at leasttwo cell pieces. The cell pieces can comprise opposing half-cell piecesand/or half multi-cell pieces.

At step 1015, the cell pieces can be coated with one or more layers ofmagnesium and boron. The coated cells are then heat treated with a heattreatment cycle as illustrated at step 1020. The heat profile of theheat treatment cycle can range from 400-700 degrees C. The heattreatment allows the Mg to mix with copper. The Mg then reacts with theboron to form superconducting MgB₂. The cell pieces can then be joinedwith longitudinal seams at step 1025 in order to form a superconductingRF resonating cavity. The method ends at step 1030.

In an alternative embodiment, the cell pieces can be joined before theheat treatment cycle. In another alternative embodiment, the heattreatment to mix Mg with copper can precede the coating with boron. Thecell pieces with Mg mixed with copper can then be re-coated with boron.The re-coated pieces can be heat treated with a profile between 600 and900 degrees C., which allows Mg to react with boron to formsuperconducting MgB₂.

FIGS. 11-18 provide flow charts of methods for forming RF resonatingchambers associated with embodiments disclosed herein for a selection ofmaterials and configurations

FIG. 11 illustrates a method 1100 for forming an RF resonating chamberof non-superconducting copper. The method begins at step 1105. At step1110, at least two RF chamber pieces can be formed from high puritycopper. At step 1115, a brazing agent can be applied to the joiningsurfaces of the respective RF chamber pieces where they will be joined.The joint between the joining surfaces is oriented to be longitudinal,as disclosed herein. At step 1120, the copper RF chamber pieces can bejoined and brazed to from an RF resonating chamber. In other embodimentssoldering, TIG welding, laser welding, electron-beam welding, diffusionbonding, friction welding, and/or other joining techniques can be usedto longitudinally join the RF chamber pieces. The method ends at step1125.

FIG. 12 illustrates a method 1200 for forming a superconducting RFresonating chamber using copper and niobium. The method begins at step1205. At step 1210, at least two RF chamber pieces can be formed fromhigh purity copper. At step 1215, the joining surfaces of the chamberpieces can be masked, before a niobium coating is applied at step 1220.The niobium coating can be applied via vacuum plasma spray, physicalvapor deposition, sputtering, ion-beam deposition, evaporation, laserablation, and/or other such coating techniques. The joining surfaces ofthe chamber pieces can be unmasked at step 1225. At step 1230, a brazingagent can be applied to the joining surfaces of the respective RFchamber pieces where they will be joined. The joint between the joiningsurfaces is oriented to be longitudinal, as disclosed herein. At step1235, the chamber pieces can be joined and brazed to from asuperconducting RF resonating chamber. The method ends at step 1240.

FIG. 13 illustrates a method 1300 for forming a superconducting RFresonating chamber using copper and Nb₃Sn. The method begins at step1305. At step 1310, at least two RF chamber pieces can be formed fromhigh purity copper. At step 1315, the joining surfaces of the chamberpieces can be masked, before an Nb₃Sn coating is applied at step 1320.In other embodiments, it should be understood that other superconductingmaterials may alternatively or additionally be applied at step 1315. Thesuperconducting coating can be applied via physical vapor deposition.The joining surfaces of the chamber pieces can be unmasked at step 1325.At step 1330, a brazing agent can be applied to the joining surfaces ofthe respective RF chamber pieces where they will be joined. The jointbetween the joining surfaces is oriented to be longitudinal, asdisclosed herein. At step 1335, the chamber pieces can be joined andbrazed to from a superconducting RF resonating chamber. In otherembodiments, soldering, TIG welding, laser welding, electron-beamwelding, diffusion bonding, friction welding, and/or other joiningtechniques can be used to longitudinally join the RF chamber piecesaccording to the choice of superconducting material used to coat the RFchamber pieces. The method ends at step 1340.

FIG. 14 illustrates a method 1400 for forming a superconducting RFresonating chamber using tin and Nb₃Sn. The method begins at step 1405.At step 1410, at least two RF chamber pieces can be formed from highpurity copper. At step 1415, tin metal can be applied to the RF chamberpieces by evaporation and/or physical vapor deposition. Application oftin serves as a soldering or brazing agent when the RF chamber piecesare later joined and sealed. Next, at step 1420, the RF chamber piecesare subject to a heat treatment cycle of between 210 and 400 degreesCelsius to from a bronze phase, which is a solid solution of copper intin (also known as the “alpha phase” in a copper-tin phase diagram).

The joining surfaces of the chamber pieces can be masked at step 1425,before a niobium coating is applied at step 1430. The niobium coatingcan be applied via vacuum plasma spray and/or physical vapor deposition.The joining surfaces of the chamber pieces can be unmasked at step 1435.At step 1440, a high-temperature brazing agent can be applied to thejoining surfaces of the respective RF chamber pieces where they will bejoined. The joint between the joining surfaces is oriented to belongitudinal, as disclosed herein. At step 1445, the chamber pieces canbe joined and brazed or welded to from a superconducting RF resonatingchamber. The assembled RF resonating chamber can then be subject to asecond heat treatment cycle at step 1450, where the assembly is heated atemperature between 630 and 700 degrees Celsius for two or more hours.The method ends at step 1455.

FIG. 15 illustrates a method 1500 for forming a superconducting RFresonating chamber using layers of niobium and bronze. The method beginsat step 1505. At step 1510, at least two RF chamber pieces can be formedfrom high purity copper. The joining surfaces of the chamber pieces canbe masked at step 1515, before a first coating of bronze is applied atstep 1520 via vacuum plasma spray. Next at step 1525, a coating ofniobium is applied via vacuum plasma spray. It should be appreciatedthat other deposition methods such as physical vapor deposition may beused for providing the coating of bronze and niobium. The bronze coatingshould be at least three times thicker than the niobium coating toachieve the best properties, but other thicknesses may also be used incertain designs. The coating thickness should preferably be between 10and 100 micrometers, although other thicknesses are also possible. Thejoining surfaces of the chamber pieces can be unmasked at step 1530. Atstep 1535, the chamber pieces can be joined to from a superconducting RFresonating chamber. The assembled RF resonating chamber can then besubject to a heat treatment cycle at step 1540, where the assembly isheated to a temperature between 630 and 700 degrees Celsius for two ormore hours. The heat treatment cycle produces Nb₃Sn and activates abrazing agent to seal the joined RF resonating chamber. The method endsat step 1545.

FIG. 16 illustrates a method 1600 for forming a superconducting RFresonating chamber using layers of niobium and bronze. The method beginsat step 1605. At step 1610, at least two RF chamber pieces can be formedfrom high purity copper. The joining surfaces of the chamber pieces canbe masked at step 1615. A first coating of niobium can be applied viavacuum plasma spray at step 1620, a first coating of bronze is appliedat step 1625 via vacuum plasma spray, and a second coat of niobium canbe applied via vacuum plasma spray at step 1630. The first niobiumcoating should be thicker than the second niobium coating and the bronzecoating is preferably three times thicker than the second niobiumcoating (other coating thicknesses are possible in other embodiments).The joining surfaces of the chamber pieces can be unmasked at step 1635.At step 1640, a high temperature brazing agent can be applied to thejoining surface of the RF resonating chamber pieces. The chamber piecescan be joined to from a superconducting RF resonating chamber at step1645. The assembled RF resonating chamber can then be subject to a heattreatment cycle at step 1650, where the assembly is heated a temperaturebetween 630 and 700 degrees Celsius for two or more hours. The heattreatment cycle produces Nb₃Sn and activates a brazing agent to seal thejoined RF resonating chamber. The time and temperature of the heattreatment should be sufficient to consume the entire second layer ofniobium, which results in the formation of Nb₃Sn. The first niobiumlayer serves as a diffusion barrier. The method ends at step 1655.

FIG. 17 illustrates a method 1700 for forming a superconducting RFresonating chamber. The method begins at step 1705. At step 1710, atleast two RF chamber pieces can be formed from high purity copper. Thejoining surfaces of the chamber pieces can be masked at step 1715.Magnesium can be applied to the copper via evaporation or physical vapordeposition at step 1720. The joining surfaces of the chamber pieces canbe unmasked at step 1725, and then a heat treatment cycle can be appliedto the shell chambers at step 1730. The heat treatment cycle ispreferably applied at 400 to 500 degrees Celsius in order to formmagnesium bronze. The joining surfaces of the chamber pieces can againbe masked at step 1735. Boron can be applied to the chambers at step1740 via physical vapor deposition. The joining surfaces of the chamberpieces can be unmasked at step 1745. A second heat treatment cycle canbe applied at step 1750, where the shells are heated to a temperaturebetween 630 and 700 degrees Celsius for one hour (other times mayalternatively be used). At step 1755, a high temperature brazing agentcan be applied to the joining surface of the RF resonating chamberpieces. The chamber pieces can be joined to from a superconducting RFresonating chamber at step 1760. In this case, the superconductor formedis MgB₂. The method ends at step 1765.

FIG. 18 illustrates a method 1800 for forming a superconducting RFresonating chamber. The method begins at step 1805. At step 1810, atleast two RF chamber pieces can be formed from high purity copper. Thejoining surfaces of the chamber pieces can be masked at step 1815. Atstep 1820, the interior surfaces of the RF chamber shell pieces can bepolished. Next at step 1825, a layer of lanthanum zirconate can beapplied via metal-organic deposition. This step can be performed at hightemperature. At step 1830, a second layer of lanthanum zirconate can beapplied via metal-organic deposition, again at high temperature. Itshould be appreciated that other materials include lanthanum aluminate,strontium titanate, magnesium oxide, and other materials. A coating ofYBCO superconductor can then be applied via metal-organic deposition atstep 1835, again at high temperature. The joining surfaces of thechamber pieces can be unmasked at step 1840. A brazing agent is appliedto the joining surface of the RF resonating chamber pieces at step 1845.The chamber pieces can be joined to from a superconducting RF resonatingchamber at step 1850. Airflow can then be applied through the formedcavity interior while the exterior of the cavity is heated to atemperature of or around 400 degrees Celsius at step 1855. Thisoptimizes the YBCO Properties. The method ends at step 1860.

Reactions described above takes place at temperatures as low as 600° C.Direct reaction of Sn and Nb to produce Nb₃Sn of good quality requirestreatment at 1100° C. or higher. The presence of copper suppressesthermodynamic equilibrium with unwanted Nb₆Sn₅ and NbSn₂ which otherwiseoccur during reactions below 910° C.

Longitudinal copper cavities can incorporate copper-magnesium and boronlayers to produce MgB₂ as the superconductor coating after reactionabove approximately 700° C.

In summary, the embodiments disclosed herein provide improved methodsand systems for manufacturing RF resonant cavities. As illustrated inthe methods disclosed herein, the convenience of line-of-sightdeposition permits many different materials and combinations ofmaterials to be applied, allowing the cavity manufacture to be easilytailored to suit the parameters of operation.

Because superconductors provide substantially increased efficiency inoperating a cavity (with a significant trade-back of efficiency relatedto cooling requirements), access to a variety of superconductingmaterials permits flexibility to adjust efficiency, refrigerationtrade-back, material cost, and other factors to suit an application.

For cavity resonators that accelerate electron beams with high dutyfactor, substantial heat can build up on the cavity walls. Copper,aluminum, or other such thermal conductor can be used as theelectrically conductive material used to facilitate heat conduction toan external cooling source, where heat conduction can be many timesbetter than the heat conduction of the superconducting material. Commonmetals with high electrical and thermal conductivity are alsoinexpensive compared to most superconducting materials. Using conductivemetals, as described herein, for the majority of part-cavity pieces mayreduce cost, by replacing expensive material required for the cavitystructure to be formed from a bulk superconductor, such as niobiummetal.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. In certainembodiments, accelerating cavities with longitudinal seams are formedfrom, or coated with, a superconducting material. In some embodiments,such cavities are formed from copper, aluminum, tin, or copper alloys(including bronze) which serve as the electrically conductive material.Longitudinal seams can be used to seal longitudinally divided copper (orother such material) cavities that incorporate niobium metal as thesuperconductor. In other embodiments, longitudinal seams seallongitudinal copper cavities that incorporate Nb₃Sn as thesuperconductor by direct application. In still other embodiments,longitudinal seams seal longitudinal copper cavities that incorporatebronze, niobium, and/or tin layers to produce Nb₃Sn as thesuperconductor coating after reaction.

In certain embodiments, the cavities as described above compriseselected chambers (cells) that contain the superconductor. This caninclude hybrid mixed superconductor associated with normal metalcavities; traveling-wave cavities; and drift cavities with sidechambers.

In other embodiments, cavities as described above can include othercoatings that are applied to the superconductor. Such coatings canmodify the secondary electron emission properties of the cavity; canmodify the work function or multipactoring behavior; and can includedielectric coatings.

In certain embodiments, patterning or lithographic techniques can beapplied to the superconductors in the cavities described above to tailorelectric field configuration within the cavity.

Based on the foregoing, it can be appreciated that a number ofembodiments, preferred and alternative, are disclosed herein. Forexample, in one embodiment, a method for fabricating acceleratorcavities comprises forming at least two pieces of an RF resonatingcavity and joining the at least two pieces of the RF resonating cavitywith a longitudinal seal thereby forming an RF resonating cavity. In anembodiment, the at least two pieces of the RF resonating cavity compriseat least one of aluminum, copper, tin, and copper alloys.

In an embodiment, the method further comprises coating the at least twopieces of the RF resonating cavity. The coating can comprise asuperconductor. The superconductor comprises one of niobium, MgB₂, andNb₃Sn.

In an embodiment, the method further comprises heat treating the RFresonating cavity. Heat treating the RF resonating cavity furthercomprises heating the RF resonating cavity to a temperature ranging from600° C. to 1100° C.

In another embodiment, the method further comprises applying one ofpatterning and lithographic processes to surfaces of the RF resonatingcavity to tailor an electric field configuration therein.

In another embodiment, a system comprises at least two pieces of an RFresonating cavity and a longitudinal seal joining the at least twopieces of the RF resonating cavity thereby forming an RF resonatingcavity. In an embodiment of the system, the at least two pieces of theRF resonating cavity comprise at least one of aluminum, copper, tin, andcopper alloys.

In an embodiment, the system further comprises a coating applied to theat least two pieces of the RF resonating cavity. The coating cancomprise a superconductor. The superconductor can comprise one ofniobium, MgB₂, and Nb₃Sn.

In another embodiment of the system, a heat treatment cycle is appliedto the RF resonating cavity. The heat treatment cycle further comprisesheating the RF resonating cavity to a temperature ranging from 600° C.to 1100° C.

In another embodiment of the system, a pattern formed in at least onesurface of the RF resonating cavity can be applied via one of patterningand lithographic processes and is configured to tailor an electric fieldconfiguration therein.

In yet another embodiment, a method for fabricating accelerator cavitiescomprises forming at least two pieces of an RF resonating cavity,applying a superconducting coating to at least one surface of the atleast two pieces of the RF resonating cavity, and joining the at leasttwo pieces of the RF resonating cavity with a longitudinal seal therebyforming an RF resonating cavity.

In an embodiment, the at least two pieces of the RF resonating cavitycomprise at least one of aluminum, copper, tin, and copper alloys.

In an embodiment, the superconductor comprises one of niobium, MgB₂, andNb₃Sn.

An embodiment of the method further comprises heat treating the RFresonating cavity, wherein heat treating the RF resonating cavityfurther comprises heating the RF resonating cavity to a temperatureranging from 600° C. to 1100° C.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also, itwill be appreciated that various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art which are also intended tobe encompassed by the following claims.

What is claimed is:
 1. A system comprising: two cavity pieces of an RFresonating cavity; and a longitudinal seam joining said two cavitypieces of said RF resonating cavity, wherein the longitudinal seam isconfigured such that the longitudinal seam intersects a cavity openingat a perpendicular angle, thereby forming the RF resonating cavity,wherein during operation of the RF resonating cavity, an RF current doesnot cross the longitudinal seam.
 2. The system of claim 1 wherein saidat least two pieces of said RF resonating cavity comprise at least oneof: aluminum; copper; tin; and copper alloys.
 3. The system of claim 1further comprising: a coating applied to said at least two pieces ofsaid RF resonating cavity.
 4. The system of claim 3 wherein said coatingcomprises a superconductor.
 5. The system of claim 4 wherein saidsuperconductor comprises one of: niobium; MgB₂; and Nb₃Sn.
 6. The systemof claim 1 further comprising: a heat treatment cycle applied to said RFresonating cavity.
 7. The system of claim 6 wherein heat treatment cyclefurther comprises: heating said RF resonating cavity to a temperatureranging from 600 ° C. to 1100° C.
 8. The system of claim 7 furthercomprising: a pattern formed in at least one surface of said RFresonating cavity applied via one of patterning and lithographicprocesses configured to tailor an electric field configuration therein.